The present invention relates to an elevator installation with a car and equipment for detecting a car position, as well as to a method of operating such an elevator installation.
It is known to determine the car position of an elevator installation in order to derive from this information control signals which are further used by the elevator control. Thus, German Utility Model DE 9210996 U1 teaches equipment for determining the car position by a magnet strip and a magnet head for reading the magnet strip. The magnet strip has a magnetic coding and extends along the entire travel path of the car. The magnet head fastened to the car contactlessly reads the coding. A car position is determined from the read-off codes.
A further development of this known equipment is disclosed in Patent Specification WO 03011733 A1. According to the teaching of this patent specification the coding of the magnet strip consists of a plurality of code marks arranged in a row. The code marks are magnetized either as a south pole or as a north pole. Several successive code marks form a code word. The code words are in turn arranged in a row as a code mark pattern with binary pseudo random coding. Each code word thus represents an absolute car position.
For scanning the magnetic fields of the code marks the equipment of the Patent Specification WO 03011733 A1 comprises a sensor device with several sensors, which enable simultaneous scanning of several code marks. The sensors convert the different poling of the magnetic fields into corresponding binary information. For south poles it issues a binary value “0” and for north poles a bit value “1”. This binary information is evaluated by an evaluating unit of the equipment and processed into an absolute position statement comprehensible to the elevator control and used by the elevator control as control signals.
Patent Specification WO 03011733 A1 further teaches the use of small sensors of three millimeter length, which are arranged in two mutually adjacent tracks so that two sensors come to lie on the length of a code mark. Due to this periodicity of the sensors which is twice as high as that of the code marks the sensors can clearly detect a transition between differently poled code marks as a zero transition of the magnetic field.
In the detection of the magnetic field of the code marks the resolution of the absolute car position is equal to the length of one code mark, i.e. four millimeters. In detection of the transition between differently poled code marks the resolution of the absolute car position is substantially better and amounts to 0.5 millimeters.
A disadvantage of the equipment of the Patent Specification WO 03011733 A1 is firstly that the strength of the magnetic field in normal direction above the code marks rapidly decreases and the sensors therefore have to be positioned at a small spacing of three millimeters above the code marks. A further disadvantage of this equipment is that the sensors have to be positioned centered above the code marks with a high degree of accuracy of +/− one millimeter. The sensor device above the code pattern has to be guided in a complicated manner for a sufficiently large security and adequate reliability of the elevator installation. This is costly. The cost connected therewith is very large particularly in the case of high car speeds of ten m/sec.